1. Field of the Invention
The present invention relates generally to a method and apparatus for completing articles of manufacture from preformed components and, more particularly, to a method and apparatus for infiltrating preformed porous components comprising particulates and that may have been formed by a method of layered-manufacturing. The method and apparatus disclosed has particular applicability for large and/or heavy articles of manufacture formed of such components or assemblies of such components that, because of their mass, may require some form of structural support during the sintering and subsequent infiltration process.
2. State of the Art
Various methods of forming metal components have been known for generations, including conventional methods such as casting, forging, and machining. However, because of a need to produce more complex metal components, conventional techniques have proved to be inadequate for some applications, such as the manufacture of drill bits for subterranean drilling, and thus have actually limited the degree of complexity of such manufactured components.
One method that is not so limited in its ability to produce very complex components is layered-manufacturing as disclosed in U.S. Pat. No. 5,433,280, assigned to the assignee of the present invention and incorporated herein for all purposes by this reference. The ""280 patent discloses a method of fabricating a drill bit body or 30 bit component in a series of sequentially superimposed layers or slices. As disclosed, a drill bit is designed as a three-dimensional xe2x80x9csolidxe2x80x9d model using a computer-aided design (CAD) program, which allows the designer to size, configure and place all internal and external features of the bit, such as (by way of example) internal fluid passages and bit blank voids, and external cutter sizes, rakes and locations as well as the height, thickness, profile and orientation of lands and ridges on the bit face and the orientation, depth and profile of waterways on the bit face and junk slots on the bit gage. The CAD program then numerically xe2x80x9cslicesxe2x80x9d the solid model into a large number of thin planar layers.
After the mathematical slicing or layering is performed by the CAD program, a horizontal platen is provided on which a granular or particulate material such as a tungsten carbide coated with a laser-reactive bonding agent such as a polymer, a resin, and/or a low melting point metal such as Wood""s metal or a lead alloy, or tungsten carbide intermixed with such a laser-reactive bonding agent is deposited in a thin, uniform layer. A finely focused laser, a focused light source such as from an incandescent or discharge type of lamp, or other energy beams, programmed to follow the configuration of the lowermost or base section or layer of the bit body, is directed on the powder layer to melt the bonding agent and bond the metal particles together in the areas of the layer represented as solid portions of the bit in the model. Another layer of powder is then uniformly deposited over the first, now-bonded layer, after which the metal particles of the second layer are bonded to each other and simultaneously to the first layer by the laser. The process continues until all layers or slices of the bit, as represented by the solid numerical model, have been deposited and bonded, resulting in a mass of bonded-particulate material comprising a bit body which faithfully depicts the computer model in every dimensional respect. In areas of each layer which are not to form a part of the completed article, the laser does not traverse and bond the particles. Thus, a drill bit, or at least a bit body comprised of bonded-particulate material, may be fabricated directly from the CAD-generated solid model without the necessity of designing and fabricating molds and without the delicate, artistic hand labor currently required for bit details.
The bit body may then be placed in a furnace where it may be preheated to substantially remove the bonding agent. In such instances, certain metal powders may be at least preliminary sintered or fused, such sintering to be enhanced or completed if necessary in a later furnacing operation.
If a powdered metal coated with a bonding agent or metal intermixed with a bonding agent is employed as the particulate material as mentioned above, the resulting bit body is a porous and permeable metal mass akin to a sponge or an open-cell foam which can be imbibed with suitable hardenable infiltrants, either metallic, non-metallic, or a combination thereof, to complete the bit body. If an infiltrant in liquid form at room temperature, such as certain polymers, is employed, the bit may be mass infiltrated via capillary, gravity, and/or pressurized flow at room temperature, while if an infiltrant that is solid at room temperature is employed, the bit would be mass infiltrated by capillary, gravity, and/or pressurized flow in a furnace, induction coil, or other heating methods known in the art of fabricating matrix-type drill bits from loose tungsten carbide powders contained in a mold.
U.S. Pat. No. 5,433,280 also discloses a tungsten carbide or other suitable powder or mix of powders (either metallic or non-metallic) having desired physical characteristics for a matrix substantially uniformly premixed with a powdered polymeric (or other nonmetallic) or metallic infiltrant powder, the premix deposited in layers and the infiltrant powder at least partially fused by a laser to bond the tungsten carbide particles into a matrix and define the bit body shape. After the layering and fusing process is completed, since the infiltrant is already in place, the bit body is heated in a furnace to effect complete in situ infiltration of the matrix. In another alternative to the foregoing procedure, layers of matrix powder alternating with layers of infiltrant powder are deposited. In either case, additional infiltrant may be added during infiltration to fill any infiltrant-deprived voids in the infiltrant-consolidated metal powder matrix. If an infiltrant-coated tungsten carbide or other suitable powder or mix of powders in a layered fashion is employed, a laser may be used to melt the infiltrant coating at least enough to cohere each layer, and the completed bit body placed in a furnace for an in situ infiltration of the bit body, with additional infiltrant being provided if necessary, as noted above.
While it is known the art to infiltrate conventionally cast particulate metallic articles of manufacture, such as drill bits, with an infiltrant while still contained within their casting mold, layered-manufacturing does not require or generate a mold as a result of the manufacturing process. While it is known that relatively small size and weight components may be infiltrated in a xe2x80x9cfree-standingxe2x80x9d manner by placing the infiltrant around the component and heating until the infiltrant is imbibed or wicked into the component, the frictional properties of the layered component maintaining its configuration, such a xe2x80x9cfree-standingxe2x80x9d approach has not proved to be practical for many larger, heavier and more complex layered-manufactured components, including drill bits and bit components such as blades. During high-temperature infiltration of such a massive layered-manufactured component, when the bonding agent effectively burns away, the mass of metallic particles is left with little or no cohesiveness and thus little or no internal structural strength for self-support. The component thus tends to collapse of its own weight during infiltration. Accordingly, it would be advantageous to provide either supplemental physical or other support for the three-dimensional component structure to ensure that the article of manufacture retains its layered-manufactured configuration during the infiltration process.
Accordingly, a method and apparatus for infiltrating preformed porous components that may have been fabricated from particulates using a layered-manufacturing technique, such as the method disclosed in U.S. Pat. No. 5,433,280, is provided. The invention may be said to be applicable to preforms of bonded particulates in general, regardless of the method of fabrication of the preform. The invention has specific applicability to drill bits and other drilling-related structures as well as other non-drilling-related articles of manufacture where structural support of the article during infiltration is of concern. More specifically, this method and apparatus is useful with larger, more massive, porous preformed components and/or components having cantilevered, thin or otherwise delicate portions that are not self-supporting and which may yield from their own weight during infiltration. The method and apparatus are also applicable to infiltration of assemblies of particulate-based components and assemblies including both particulate and non-particulate (solid) components. In several of the preferred embodiments, a mold or mold-like structure is provided that rigidly and/or pliably supports the layered-manufactured component, the rigidity of the mold being dependent upon the material used to form the mold or mold-like structure.
In a preferred embodiment, once a component or component assembly has been fabricated at least partially using a method of layered-manufacturing, a castable material, such as ceramic, plaster, graphite slurry or other similar materials known in the art able to withstand the high temperatures encountered during the infiltration process, is poured around the component to provide solid structural support upon solidification of the castable material. Similarly, the component or assembly may be dipped one or more times into a castable material, such as a ceramic, plaster, or graphite slurry to form a relatively rigid material around the component. In either case, it is preferable to pre-plug any orifices or openings leading to internal passageways in the component so that castable material that may otherwise be difficult to remove therefrom does not accumulate inside the component or assembly. Such plugs may be comprised of sand, graphite particles, clay or other suitable materials known in the art.
In another preferred embodiment, the layered component or assembly may be placed in a refractory vessel with granular material packed around it up to its uppermost surface. This granular material substantially completely surrounds all surfaces of the component and may be vibrated to more densely pack the granular material. Because the granular material maintains its granular form during infiltration and is non-wettable by the infiltrant, the granular material effectively forms a xe2x80x9cpliablexe2x80x9d mold. That is, the granular material continues to provide structural support for the component during infiltration as dimensions of the component change, such as by shrinkage that may occur as the bonding agent employed to preliminarily hold the metallic particles of the component together vaporizes. Preferably, the granular material does not sinter, tack, or otherwise strengthen during the infiltration process, and thus continues to support the component substantially throughout infiltration without substantial change in its supporting physical characteristics.
In yet another preferred embodiment, a granular material that sinters, chemically reacts, or otherwise strengthens during the infiltration process could provide a more rigid mold to support the component. Such a mold would be particularly beneficial for components that undergo little or no shrinkage.
In addition, it may be sufficient that a substantially rigid mold may be employed to provide support primarily during the first stages of infiltration, wherein the metallic particles of the layered component are imbibed with a sufficient amount of infiltrant and/or sufficiently sintered so that the component can structurally support itself.
Additionally, a mold material may be selected that conforms by shrinking and/or expanding along with any shrinkage and/or expansion of the component during the infiltration process to maintain a substantially rigid but conforming support structure. Such a mold would also help prevent infiltrant material from flowing out of the component and pooling in gaps that may otherwise form between the component and the interior surface of the mold if the dimensions of the mold remain constant relative to the varying dimensions of the component during infiltration.
In yet another preferred embodiment, a support structure according to the present invention may have equal utility for a component comprised of metallic particles intermixed with particles of an infiltrant material. With such a component, it may not be necessary to leave at least one surface exposed for additional infiltrant to be imbibed into the component. Such a component, however, may require structural support similar to other components herein described.
Preferably, all of the materials used to form the support structure and/or fill any internal cavities in the component are formed from materials that are non-wettable by the infiltrant. That is, these materials do not absorb or otherwise chemically or mechanically bond to or react with the infiltrant utilized for infiltration. Rather, these materials form a barrier, because of their non-wettable quality, around the component such that the infiltrant stays contained within the component and does not bind the support structure to the component. In addition, the molds or support structures herein described are preferably formed from materials that are substantially permeable to gases and vapors generated during the infiltration process, so as to preclude the formation or retention of gas or vapor voids in the component being infiltrated.
In yet another preferred embodiment, if a wettable material is used to form the support structure, the component may be coated with an infiltrant-resistive material, such as boron nitride or other suitable materials known in the art, prior to being placed within, or surrounded by, the support material. The boron nitride may be simply sprayed or painted onto various surfaces of the component, or the component may be dipped into a container of a boron nitride suspension to form a barrier through which the infiltrant cannot flow out of the component and imbibe the wettable support structure. Thus, the non-wettable (by the infiltrant) resistive coating keeps the molten infiltrant contained within the layered component. In addition, such a coating may aid in forming a better surface finish for the component as it creates an intermediate shell to which the layered part and the infiltrant can conform during infiltration. Moreover, due to its liquid consistency, the coating fills small voids, vugs or intricately configured areas that may not be completely, intimately contacted by the surrounding support material. During the coating process, it is generally desirable to leave at least one surface uncoated so that the component has at least one non-resistive or wettable surface through which to imbibe additional infiltrant, even if infiltrant is already present in the preformed component. It is contemplated that such a resistive coating may be used in conjunction with other preferred embodiments of the present invention, whether the support material is wettable or non-wettable, to help form a better surface finish and help ensure that the infiltrant does not flow out of the component and into the support structure, pool in any voids, gaps or vugs present between the component and the support structure, or form an unwanted skin of infiltrant on the outer surface of the component.
After the layered-manufactured component has been properly supported according to the present invention, the article of manufacture and any supporting materials and/or structures can be placed within a traditional furnace, an induction coil furnace, or other heating apparatus known in the art along with an infiltrant and heated until the infiltrant melts and substantially fully permeates the article of manufacture through the free surface exposed to the infiltrant. The materials used to infiltrate the component are typically copper-based alloys containing other elements such as nickel, as known in the art of fabrication of matrix-type drill bits. However, it is contemplated that any suitable infiltrant compatible with the particulates of the component preform may be used in conjunction with the present invention.